Method of coating a substrate with magnetic ferrite film



July 27, 1965 W. L. WADE, JR

METHOD OF COATING A SUBSTRATE WITH MAGNETIC FERRITE FILM ALCO OLICSOLUTION OF FERRIC NITRATE Filed NOV. 6, 1962 MIX WITH I ALCOHOLICSOLUTION 0F AT LEAST ONE METAL NITRATE FROM THE GROUP CONSISTING OFNICKEL, ALUMINUM, ZINC AND COBALT.

PRELIMINARILY FIRE COATED SUBSTRATE AT 400C TO 700 C COOL REPEAT IMMERSI0N PRELIMINARY FIRING AND COOLING STEPS UNTIL THE DESIRED AMOUNT OFMATERIAL IS OEPOSITED FIRE COATED SUBSTRATE AT IO0OC TO ll00C FOR ONE TOFIVE HOURS TO ALIGN THE OXIDES FORMED TO THE SPINEL STRUCTURE OF THEFERRITE SOLUTION -4-IMMERSE SUBSTRATE INTO SOLUTION INVENTOR, WILLIAM L.WADE JR.

ATTORNEY.

United States Patent 3,197,334 METHOD OF CBATHNG A SUBSTRATE WETHMAGNETIC FERRITE FEM William L. Wade, Jr., Neptune, NJL, assignor to theUnited States of America as represented by the Secretary of the ArmyFiled Nov. 6, 1962, Ser. No. 235,306

3 Claims. (Cl. 117-169) (Granted under Title 35, US. Code (1952), see.256) The invention described herein may be manufactured and used by orfor the Government for governmental purposes, without the payment of anyroyalty thereon.

This application is a continuation-in-part of my'US. patent applicationSerial Number 99,5 63 filed March 31, 1961, now abandoned, for method ofmaking Magnetic Ferrite Film. This invention relates to a simple methodof making magnetic ferrite films from nitrate solution.

An object of the invention is to make magnetic ferrite films of highcompositional purity by a relatively short and simple technique.

Magnetic ferrite films are relatively new. They are adaptable for use incomputer memories, logic circuits, and microwave devices. One verypromising application of the magnetic ferrite films is in thetraveling-wave maser structure wherein their use provides for anunconditionally-stable maser amplifier. The use of magnetic ferritefilms is of distinct advantage over the use of bulk ferrite in microwavedevices at high frequencies. This is because one cannot grind solidferrite materials thin or uniform enough to fit into such devices. Themagnetic ferrite films on the other hand are suitable in these devicesas they can be coated to any thickness and be cut to any desired shape.Alternatively, the films can be of economic advantage in that thesubstrate can be cut to the desired shape beforehand and then coated.

Heretofore, many of these films have been made by the vacuum depositiontechnique of vaporizing the metals on suitablesubstrates and thenheating or rather firing the metals at high temperatures for prolongedperiods to convert the metals to oxides and alignment to the ferritefilm.

It has now been found that magnetic ferrite films of high compositionalpurity can be made by a relatively short and simple technique. Thetechnique involves the dissolving of ferric nitrate and one or morenitrates of the metals of the group of magnesium, nickel, aluminum,zinc, and cobalt in alcohol at room temperature; immersing the surfaceof a substrate in the solution; preliminary firing the coated substrateat 400 C. to 700 C. in a furnace; and succesively cooling to roomtemperature between coats. After weighing on a balance to determineexact amounts of material deposited, the coated substrate is heated to1000 C. to 1100 C. in a furnace for one to five hours to align theoxides formed to the spinel structure of the ferrite.

A fiow sheet of the process is illustrated by the drawing.

Some preferred embodiments of the invention are hereinafter described. 1

Example 1 Nickel nitrate is reacted with ferric nitrate in such amountsthat one mole is present for two moles of iron according to the reaction'ice According to the method, 86 grams (0.3 mole) of Ni(l lO .6H O and86 grams (0.2 mole) of are separately dissolved in 100 milliliters ofanhydrous ethanol, the metal concentration of these solutions being0.1735 gram and 0.1189 gram of nickel and iron, respectively permilliliter of solution. A stoichiometric ratio of the above-mentionedstock solutions is prepared by mixing 25 milliliters of the ironsolution containing 2.9725 grams of iron with 9.02 milliliters of nickelsolution containing 1.5651 grams of nickel. A fused quartz substrate isthen dipped in the stoichiometric alcoholic nitrate solution allowingthe excess to flow back. The substrate is then placed in a furnace setat 500 C. for 60 to seconds, removed, and then cooled to roomtemperature. During this preliminary heating, nitric oxide fumes evolvecausing flaking of the material at varied spots upon the surface of thefused quartz. The flakes are gently removed and the substrate redippedin the solution repeating the abovementioned procedure until an evencoat of a desired thickness is obtained. Between 0.5 and 1.0 milligramof material is deposited during each operation. The substrate is thenfired at 1000 C. for one hour to align the metallic oxides formed (thatis, Ni() and Fe O to the spinel structure of the ferrite. X-raydiffraction techniques carried out on the coated substrate indicate thatthe deposited coating corresponds to a nickel ferrite spinel structure.

An evaluation of the magnetic properties of the nickel ferrite films atmicrowave frequencies is then made. In the evaluation, microwavemeasurements are made on films deposited on quartz and aluminasubstrates having the dimensions 0.9" x 0.4" plotting attenuation versusapplied field. The resulting absorption curves show a definite activityat microwave frequencies and portray the films as being ferromagnetic.

Example 2 Magnesium nitrate is reacted with ferric nitrate in :suchamounts that one mole of magnesium is present for two moles of ironaccording to the reaction According to the method, magnesium and ironstock solutions are prepared by dissolving 43 grams (0.11 mole) of:Fe(NO .9H O in 50 milliliters of anhydrous ethanol and 43 grams (0.17mole) of Mg(NO .6H O in 50 milliliters of anhydrous ethanol. The metalconcentration of these solutions upon analysis is 0.0529 gram of ironper milliliter of solution. A stoichiometric ratio of theabove-mentioned stock solutions is prepared by mixing 15 millilitersofthe iron solution containing 1.2345 grams of iron with 5.0 millilitersof magnesium solution containing 0.2645 gram of magnesium. The remainingtechnique of obtaining the ferrite film is the same as in Example 1.X-ray diffraction techniques carried out on the coated substrateindicate that the deposited coating corresponds to a magnesium ferritespinel structure.

An evaluation of the magnetic properties of the magnesium ferrite filmsat microwave frequencies is then made.

In the evaluation, microwave measurements are madeon films deposited onquartz and alumina substrates having the dimensions 0.9" x 0.4 plottingattenuation versus applied field. The resulting absorption curves show a1,9 definite activity at microwave frequencies and portray the films asbeing ferromagnetic.

The evaluation of the magnetic properties of the nickel ferrite andmagnesium ferrite films prepared in Examples 1 and 2 as measured atmicrowave frequencies (X-band) is shown in the following table:

Magnesium nitrate is reacted with aluminum nitrate and ferric nitrate insuch amounts that one mole of mag nesium is present for every 0.4 moleof aluminum for every 1.6 mole of iron according to the reactionAccording to the method, magnesium nitrate, aluminum nitrate, andiron'nitrate stock solutions are prepared by dissolving 43 grams (0.11mole) of Fe(NO .9H O in 50 milliliters of anhydrous ethanol, 43 grams(0.17 mole) of Mg(NO .6H O in 50 milliliters of anhydrous ethanol, andan undetermined amount of Al(NO .9H O in 50 milliliters of anhydrousethanol. A stoichiometric ratio of the above-mentioned stock solutionsis prepared by mixing 15 milliliters of the iron solution containing1.9575 grams of iron with 10.07 milliliters of magnesium solutioncontaining 0.5328 gram of magnesium with 11.20 milliliters of aluminumsolution containing 0.2364 gram of aluminum. A 96 percent aluminasubstrate is then dipped in the stoichiometric alcoholic nitratesolution allowing the excess to flow back. The substrate is then placedin a furnace set at 500 C. for 60 to 90 seconds, removed, and thencooled to room temperature. During this preliminary heating, nitricoxide fumes evolve causing flaking of material at varied spots upon thesurface of the alumina. The flakes are gently removed and the substrateredipped in the solution repeating the above-mentioned procedure untilan even coat of a desired thickness is obtained. Between 0.5 and 1.0milligram of material is deposited during each operation. The substrateis then fired at 1100 C. for 1 /2 to hours to align the metallic oxidesformed (that is, MgO and 0.4Al.1.6FeO to the spinel structure of theferrite. X-ray diffraction techniques carried out on the coatedsubstrate indicate that the deposited coating corresponds to a magnesiumaluminum ferrite structure of the formula Mg(0.4Al.l.6Fe)Ol Anevaluation of the magnetic properties of the magnesium aluminum ferritefilms at microwave frequencies is then made. In the evaluation,microwave measurements are made on films deposited on 96 percent aluminasubstrates having the dimensions 0.9" X 0.4" plotting attenuation versusapplied field. The resulting absorption curves show a definite activityat microwave frequencies and portray the films as being ferromagnetic.The evaluation of the magnetic properties of the magnesium aluminumferrite films prepared in Example 3 as measured at microwave frequencies(X-band) is shown in the following table:

41. Example 4 Magnesium nitrate is reacted with zinc nitrate and ironnitrate in such amounts that one-half mole of magnesium is present forevery one-half mole of .zinc for every two moles of iron according tothe reaction According to the method, magnesium nitrate, zinc nitrate,and iron nitrate stock solutions are prepared by dissolving 43 grams(0.17 mole) of Mg(NO .6H O in 50 milliliters of anhydrous ethanol, anundetermined amount of Znfi lO h-li b in 50 milliliters of anhydrousethanol, and 43 grams (0.11 mole) of -Fe(NO .9H O in 50 milliliters ofanhydrous ethanol. A stoichiometric ratio of the above-mentioned stocksolutions is prepared by mixing 11.) milliliters of the iron solutioncontaining 1.5520 grams of iron with 3.19 milliliters of the magnesiumsolution containing 0.1689 gram of magnesium and 2.97 milliliters of thezinc solution containing 0.4542 gram of zinc. The remaining technique ofobtaining the ferrite film is the same as in Example 3. X-raydiffraction techniques carried out on the coated substrate indicate thatthe deposited coating corresponds to a magnesium zinc ferrite spinelstructure of formula (0.5Mg.0.5Zn)Fe O An evaluation of the magneticproperties of the magnesium zinc ferrite film at microwave frequencies(X- band) is then made. In the evaluation, microwave measurements aremade on a film 22.5 microns in thickness deposited on an aluminasubstrate having the dimensions 0.9 x 0.4" plotting attenuation versusapplied field. According to the evaluation, the film is found to have aresonant frequency of 9381 megacycles, a resonant applied field of 2450oersteds, and a linewidth of about 875 oersteds. This indicates definiteactivity at microwave frequencies and portrays the film as beingferromagnetic.

The alcohol solvent recited in the statement of the invention anddisclosed in Examples 1, 2, 3, and 4 above is preferred as thedispersing agent or carrier. That is, it gives proper fiow tendencies tothe film forming solution of metallic nitrates. Other solvents that aidin evaporation and dispersion of the nitrates could be used in itsplace, as for example, a hydrocarbon solvent or a lower ketone. In noinstance, it should be pointed out, is there a reaction between themetallic nitrate and the particular dispersing agent or carrierselected. Thus, for example, a metallic alcoholate is not formed whencarrying out the method.

A practical variation in the method is to initially melt the metallicnitrate and then to add just enough water to it to maintain a liquidstate. The particular dispersing agent selected can then be added tostoichiometric ratios of the stable aqueous stock solution at the timeof carrying out the method. Though this technique is not necessary tothe invention, it is of distinct advantage Where the solution resultingfrom the dispersion of the metallic nitrate directly in the alcoholwould be unstable after three to four days, as for example, in the caseof ferric nitrate.

Example 5 Nickel nitrate is reacted with zinc nitrate and iron nitratein such amounts that 0.75 mole of nickel is present for every 0.25 moleof zinc for every 2 moles of iron according to the reaction (0.75Nl.0.25Zn) Fe;0

According to the method, stock solutions of Fe(NO .9H O, Ni(NO .6H O,and Zn(NO- .6H O

are first prepared by heating grams of each metallic nitrate toliquefaction without causing decomposition.

in. l

The now liquified metallic nitrates are kept in the liquid state by theaddition of 70 milliliters of distilled water. The stock solutionsremain constant in concentration for an indefinite period. Astoichiometric ratio of these stock solutions is then measured out bymixing 30 mil liters of the iron solution containing 3.8130 grams ofiron with 726 milliliters of the nickel solution containing 1.5026 gramsof nickel and 2.13 milliliters of the zinc solution containing 0.5581gram of zinc. Methanol is then added to the resulting stoichiometricsolution in any desired amount depending on ones observation as to thethickness of deposition on the substrate being coated. A 96 percentalumina and a fused quartz substrate are then separately dipped in thestoichiometric aqueous alchoholic nitrate solution allowing the excessto flow back. The remaining technique of obtaining the ferrite films isthe same as in Example 3. X-ray difiraction techniques carried out onthe coated substrate indicate that the deposited coating corresponds toa nickel zinc ferrite spinel structure of the formula Film ResonantResonant Line- Material Thick- Fre- Applied width ness quency Field(Oersteds) (Microns) (1110.) (Oersteds) (0.75Ni.0.25Zn) F810. 22. 5 9,210 2, 000 1825 (0.75Ni.0.25Zn) F6204 22. 5 9, 378 1, 700 650(0.75Ni.0.25Zn)Fe2O4 22. 5 9, 378 1, 650 675 (0.75Ni.0.25Zn)Fe;O4 22. 59, 374 1, 600 650 22. 5 9, 384 1, e 580 22. 9, 372 1, 565 795 Thepreliminary heating in Examples 1 through 5 above can be effected withthe aid of a hot plate set on high. III such a case as is also true inExamples 1 through 5 above, both sides of the substrate are covered butonly one is needed for evaluation. Therefore, one side is removed of itscoating with acid or a razor blade.

The substrate used is not critical; all that is required is that it betemperature stable up to 1100 C. Alumina and fused quartz have beenfound to be most useful as the substrate.

In the aforementioned examples, the thickness of the coated substrate isdetermined by weighing out prescribed ing on the ionic radius of themetals, the valence of the metals, and the crystal structure of theferrite itself.

It is intended that the foregoing description be considered merely asillustrative and not in limitation of the invention as hereinafterclaimed.

What is claimed is:

1. The method of coating a substrate with magnetic ferrite film of about7 to 23 microns in thickness comprising mixing an alcoholic solution offerric nitrate with an alcoholic solution of at least one nitrate of ametal selected from the group consisting of nickel, aluminum, zinc, andcobalt in the stoichiometric proportion necessary to form the ferrite,immersing a substrate that is thermally stable up to 1100 C. into thethus prepared solution, preliminary firing the coated substrate at 400C. to. 700 C., cooling the coated substrate, repeating the immersion,preliminary firing and cooling steps until the desired amount ofmagnetic ferrite material is deposited in situ on the substrate, andfiring the coated substrate at 1000 C. to 1100 C. for one to five hoursto align the oxides formed to the spinel structure of the ferrite.

2. The method of coatinga substrate with magnetic ferrite film accordingto claim 1 wherein the alcoholic solution of ferric nitrate is mixedwith alcoholic solution of nickel nitrate and zinc nitrate.

3. The method of coating a substrate with magnetic ferrite filmaccording to claim 1 wherein the alcoholic solution of fem'c nitrate ismixed with alcoholic solution of nickel nitrate.

References Cited by the Examiner UNITED STATES PATENTS 2,906,682 9/59Fahnoe et al 252-625 2,989,478 6/61 Eckert 252-625 3,023,165 2/62 VanUitert 252-625 3,034,986 5/62 Baird et al. 252-625 3,096,206 7/ 63 Wade117-113 3,100,158 8/63 Lemaire etal 1l7-49 3,114,714 12/63 Braun et al.252-625 3,115,469 12/ 63 Hamilton 252-625 3,142,645 7/ 64 Zerbes 252-625WILLIAM D. MARTIN, Primary Examiner.

1. THE METHOD OF COATING A SUBSTRATE WITH MAGNETIC FERRITE FILM OF ABOUT7 TO 23 MICRONS IN THICKNESS COMPRISING MIXING AN ALCOHOLIC SOLUTION OFFERRIC NITRATE WITH AN ALCHOLIC SOLUTION OF AT LEAST ONE NITRATE OF AMETAL SELECTED FROM THE GROUP CONSISTING OF NICKEL, ALUMINUM, ZINC, ANDCOBALT IN THE STOICHIOMETRIC PROPORTION NECESSARY TO FORM THE FERRITE,IMMERSING A SUBSTRATE THAT IS THERMALLY STABLE UP TO 1100*C. INTO THETHUS PREPARED SOLUTION, PRELIMINARY FIRING THE COATED SUBSTRATE AT 400*C. TO 700*C., COOLING THE COATED SUBSTRATE, REPEATING THE IMMERSION,PRELIMINARY FIRING AND COOLING STEPS UNTIL THE DESIRED AMOUNT OFMAGNETIC FERRITE MATERIAL IS DEPOSITED IN SITU ON THE SUBSTRATE, ANDFIRING THE COATED SUBSTRATE AT 1000*C. TO 1100*C. FOR ONE TO FIVE HOURSTO ALIGN THE OXIDES FORMED TO THE SPINEL STRUCTURE OF THE FERRITE.